1. Field of the Invention
The present invention relates to a heat transport device used for cooling electronics equipment, for example.
2. Description of the Background Art
To meet requirements for reliability, lightweight design, and low acoustic noise performance, a heat pipe having no moving parts, unlike pumps, has conventionally been used as a heat transport device for cooling electronics equipment, for example. It has however become difficult in recent years to cool electronic and other types of equipment by using heat pipes as a result of a rapid increase in the amount of heat radiated from the equipment.
In addition, as it is fairly difficult to control the temperature with a heat pipe, there has been a pending need for a heat transport device which allows easy temperature control.
Under these circumstances, new heat transport devices have recently been developed taking into consideration low acoustic noise performance and good temperature controllability.
One of such conventional heat transport devices is disclosed in Japanese Laid-open Patent Publication No. H7-286788, in which a pair of flat headers are interconnected by small-diameter tubes and a liquid is sealed inside the heat transport device, leaving a gas phase portion at one end of a fluid channel. The fluid channel is formed of fins provided inside the headers, and a capillary tube equipped with a heating unit, such as an electric heater, is connected to a particular part of one header. In this heat transport device, a power source supplies a voltage of a pulse-shaped waveform to the heating unit to heat the liquid inside the capillary tube in a steplike fashion, eventually causing the liquid to bump. This produces the effect of a so-called bubble lift pump, like the one shown in FIG. 1 appended to the aforementioned Japanese Laid-open Patent Publication No. H7-286788. In that device, the liquid is driven by a rapid pressure increase as a result of evaporation at one end of the fluid channel, while volumetric changes are absorbed by the gas phase portion at the other end of the fluid channel.
The aforementioned conventional heat transport device has a problem that its heat transportation and heat radiating capacities are low. This is because the conventional heat transport device is of a type which dissipates heat by driving the liquid as a result of a small-scale oscillation of the liquid within a capillary tube by means of a bubble lift pump.
Although the liquid used as a working fluid should preferably have properties suited to a bubble lift pump as well as good heat transfer and flow characteristics, it has so far been extremely difficult to satisfy all these requirements. In other words, there has been a problem that it is difficult to increase the amplitude of oscillation and reduce the period of oscillation of the working fluid for improving the performance of the bubble lift pump and to improve the heat transfer and flow characteristics of the working fluid.